Re: Web Crypto Spec Updates for ArrayBufferView, ArrayBuffer, and Streams

Le 23/04/2013 11:16, Ryan Sleevi a écrit :
>
>
> On Apr 23, 2013 12:37 AM, "Israel Hilerio" <israelh@microsoft.com 
> <mailto:israelh@microsoft.com>> wrote:
> >
> > WG,
> >
> > In the IE team we believe that defining overload methods that use 
> ArrayBuffer for the operations below make it easier for developers to 
> use the APIs without having to be constantly creating new objects or 
> casting. From our perspective there is no internal difference on how 
> ArrayBuffer or ArrayBufferViews are handled internally.
> >
> > In addition, the table below contains some proposed new methods to 
> process Streams. This would optimized the memory footprint of the 
> operations.  The expectations is that for each of the Stream methods 
> we would have a stream result from which developers could read 
> information.
> >
> > See Attachment #1 (table1.html)
> >
> > We expect the following processing to take place as part of the Streams:
> > 1. Open a stream
> > 2. Pass the streams as input
> > 3. Create output stream
> > 4. Read data from input stream when available
> > -->Input buffer sizes are defined by the UA
> > 5. Process the data from input stream
> > 6. Put processed data into output stream
> > 7. Generate and send progress event
> > 8. If the stream is not done, goto step 4.
> > 9. Continue normal processing of data
> >
> > We also believe it is better to return an ArrayBuffer type for the 
> operations below because it avoids the implicit type cast we would 
> have to do with an ArrayBufferView.  In other words, when returning an 
> ArrayBufferView, we methods need to cast the ArrayBufferView to a 
> specific type (e.g. Uint8Array, Int8Array, Int16Array, Uint16Array, 
> etc.).  Unfortunately, there is not enough information provided by the 
> API usage to guess correctly at the correct view type.
> >
> > In addition, to avoid the potential casting of ArrayBuffer into 
> ArrayBufferView we believe it would be useful to create a new type 
> called AlgorithmInputData:
> > -->typedef (ArrayBuffer or ArrayBufferView) AlgorithmInputData;
> >
> > This would allow the various input dictionaries to be able to 
> support input variables with either ArrayBufferView or ArrayBuffer.
> >
> > Our proposal is to change the following Algorithm result to 
> ArrayBuffers (empty fields are unaffected).
> >
> > See attachment #2 (table2.html)
> >
> > Thanks,
> >
> > Israel
>
> Thanks for the feedback, Israel.
>
> Can you provide more explanation about these proposed changes.
>
> This seems inconsistent with the work going on in WebApps to *unify* 
> the API designs on ArrayBufferViews (e.g. XHR and FileAPI as two 
> examples). This also conflicts with the feedback received from both 
> Mozilla and Google when early versions of the API did support such 
> overloads that such overloads were a bad design. Given the work going 
> on in other WGs to avoid such overloads, it would be helpful to better 
> understand the concerns presented here, especially given that 
> ArrauBufferViews require no copying of data to create.
>

Unless there are some changes that will happen in the future that I am 
not aware of, WebSockets are using ArrayBuffers.

> The WG also specifically agreed that Streams would NOT be a v.1 
> deliverable. While useful, the lack of adequate progress of the 
> Streams API in the past year is a clear sign that it lacks the 
> standards maturity to couple to this spec. The proposed Streams API in 
> WebApps already suffers concerns as it relates to performance and the 
> "pull" nature of data. Our past call agreed specifically to drop any 
> such deliverable from v.1 of the API - in order to make continued 
> progress.
>
> The choice of ArrayBufferView for the result, rather than ArrayBuffer, 
> may be viable. Alternatively, DataView seems equally viable, while 
> maintaining the ArrayBufferView semantics, which seems friendlier for 
> callers.
>

Right now I don't have a preference between ArrayBuffer and 
ArrayBufferView but as far as streaming is concerned (if applicable 
now), then most likely DataViews will be used (because of the endianness 
aspect of Typed Arrays), DataViews are more friendly but some might want 
to use [] (Typed Arrays) to read the buffers, and if general 
ArrayBufferViews are used then to instanciate a DataView you must do it 
with ArrayBufferView.buffer's ArrayBuffer, then maybe ArrayBuffer covers 
more cases (not withstanding the feedback of Google and Mozilla that you 
mention above and that we don't know).

> Cheers,
> Ryan
>

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